Astronomy and Astrophysics, volume 394, 107-113 (2002/10-4)
Discovery of new highly excited OH sources in regions of high-mass star formation.
BAUDRY A. and DESMURS J.F.
Abstract (from CDS):
We have carried out sensitive observations of the highly excited 2 Π3/2, J7/2 state of OH (290K above the ground-level) at 13441MHz (F=4-4) and 13435MHz (F=3-3) in both right and left circular polarizations with the Effelsberg 100-m telescope. Our sample included 27 compact or ultra-compact HII regions. Most of them have been selected from our previous J5/2 OH maser survey of star-forming regions taken from the IRAS point-source catalog. We have observed weak 2 Π3/2, J7/2, F=4-4 and 3-3 absorption in 7 sources and discovered 3 new weak F=4-4 maser sources at 13441MHz in addition to W3(OH). The new sources, 20081+3122 (ON1), 21413+5442 and G11.90-0.14, are 50 to 100 times or more weaker than the 13441MHz peak flux density observed in W3(OH). 21413+5442 and G11.90-0.14 exhibit extremely narrow velocity extents of the order of 0.4km/s. However, in ON1 there are two groups of narrow velocity features separated by about 14km/s; these two groups are also observed in lower rotational levels and suggest complex kinematics in the envelope of the young ultra-compact HII region. Apart from a very weak, polarized, and narrow J7/2, F=3-3 emission feature lying on the red wing of the 13435MHz absorption feature in W3(OH) no J7/2, F=3-3 emission was discovered. We conclude that the 13441MHz OH maser emission from W3(OH) remains exceptionally strong but not unique. In contrast with the J5/2, 6035MHz maser emission observed in a large number of star-forming regions, J7/2, 13441MHz emission is not widespread. This is expected from OH maser theory, and because the involved J7/2 levels are high in the OH energy ladder and not directly connected to the ground-state.
ISM: HII regions - ISM: molecules - masers - stars: formation
G 309.9+0.48 = GAL 309.9+00.5. In table 1, G 11.80-0.14 = GPSR5 11.903-0.141, G 0.66-0.03 = [WBH98] 17441-2822.
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